The present invention is related to power supplies, and in particular to voltage converters.
Electrical power requirements are typically satisfied by deploying one or more power supplies in relation to a particular system. For example, telecommunication and data communication systems often employ power supplies deployed in relation to an Intermediate Bus Architecture (IBA). In some such cases, the IBA based system includes a front end AC-DC power supply that generates a DC voltage. This DC voltage is supplied to the input of an Intermediate Bus Converter (IBC) that provides isolation and converts the input voltage to a lower level DC voltage supplying numerous so called point-of-load regulators (POLs). The non-isolated POLs provide required supply voltages to specific digital or analog electronic functional blocks. The POLs are generally located close to the related electronic blocks to provide highest quality supply voltages.
The aforementioned IBC may be implemented using one of the topologies depicted in FIGS. 1a-1c. In particular, FIG. 1a shows a forward type full-bridge voltage converter topology 110, FIG. 1b shows a half-bridge voltage converter topology 120, and FIG. 1c depicts a push-pull voltage converter topology 130. Depending on input voltage range and output voltage tolerances, the IBC can be regulated with feedback loop taken from its output voltage, semi-regulated by input voltage feed-forward, or simply unregulated. Unregulated IBC implementations are often more cost effective, and generally operate at a maximum duty cycle for highest efficiency and power density.
Existing unregulated voltage converters exhibit various performance limits. For example, before a primary side transistor is turned on, one or more transistors used for rectification in the secondary side must be turned off. Where the transistors on the secondary side remain on while the primary side transistors are turning on, a current overshoot occurs on the primary and secondary sides limited only by the leakage inductance of the transformer and transformer winding resistances. To avoid this problem, existing unregulated voltage converters enforce a predetermined OFF time between the switching of transistors on the primary side and those of the secondary side that is fixed over the load range of the voltage converter. This predetermined limit is selected to allow avoidance of overshoot during both high load current operation and low load current operations. Such an approach offers protection from the overshoot condition, but results in an increased OFF time during nominal loading. This results in increased conduction of the body diode of the transistors on the secondary side and a corresponding increase in conduction losses. Further, such an increased OFF time causes a decrease in effective duty cycle and a corresponding decrease in an output voltage of and unregulated voltage converter. In some cases, an additional snubber circuit protection is used and/or higher voltage rated transistors to reduce the impact of any overshoot. Such an approach, however, is costly in terms of both components and size.